class_docstr: Maps policy IDs to Policy objects.
  
  Thereby, keeps n policies in memory and - when capacity is reached -
  writes the least recently used to disk. This allows adding 100s of
  policies to a Algorithm for league-based setups w/o running out of memory.
docstr: Returns the value for the given key or None if not found.
docstr_tok: ["Returns","the","value","for","the","given","key","or","None","if","not","found","."]
code: def get(self, key: PolicyID):
      """Returns the value for the given key or None if not found."""
      if key not in self._valid_keys:
          return None
      return self[key]
  
imports: from collections import deque
  import threading
  from typing import Dict, Set
  import logging
  import ray
  from ray.rllib.policy.policy import Policy
  from ray.rllib.utils.annotations import override
  from ray.rllib.utils.deprecation import deprecation_warning
  from ray.rllib.utils.framework import try_import_tf
  from ray.rllib.utils.threading import with_lock
  from ray.rllib.utils.typing import PolicyID
  from ray.util.annotations import PublicAPI
label_desc: Use image node_id 10 for calling the PolicyMap obj's underlying member method code with example usage: obj.get(key) and returns: self, None